Apparatus for coating metals



' (No Model.)

B. I. BRADDOCK & D. A. RITCHIE.

APPARATUS FOR COATING METALS. No. 311,284.

Patented Jan. 27, 1885.

.h .HW f m V/V/M /A e W y W 7 VW 6 Unrrnn drains Aren't l l lCEQ EDlVARDI. BRADDOGK, OF MEDFORD, AND DAVID A. RITCHIE, OF CHELSEA,MASSACHUSETTS.

APPARATUS FOR COATENG METALS.

SPECIFICATION forming part of Letters Patent No. 311,29 dated January27, 1885.

' Application filed April 28, 1884. (No model.)

To all whom it may concern:

Be it known that we, EDWARD I. BRAD- DOCK, of Medford, county ofMiddlesex, and DAVID A. RITCHIE, of Chelsea, county of Suffolk, State ofMassachusetts, have invented an Improvement in Apparatus for CoatingMetals, of which the following description, in connection with theaccompanying drawing, is a specification, like letters on the drawingrepresenting like parts.

Our invention relates to an apparatus for coating metals, it beingespecially intended for galvanizing iron, and is shown embodied in anapparatus especially adapted for dipping or coating long articles, suchas iron rods or bars or sheet-metal tubing such as employed forwater-conductors and similar purposes.

Iron, as heretofore usually practiced, has been galvanized or coatedwith zinc by dipping the iron, after having its surface previouslycleaned by the action of an acid, in a bath of melted zinc contained ina tank of sufiicient size to receive the said articles, and in somecases the articles are previously tinned or coated with some othermetal. As the article has to be wholly immersed, the tanks have been imade very large when articles having verylarge dimensionsas sheet-metalpipe or long rods or barshave been treated, and such large tanks andvessels are very costly and contain a'verylarge mass of molten metal,the whole of which must be maintained at the necessary heat to keep itin a molten state. Articles that are coated in this manner, as a generalthing, have only one large dimension, or are long and slender rods ortubes, or long thin sheets; and the object of our invention is toprovide an apparatus for dipping such a1- ticles with the leastexpenditure of heat, and with a comparatively small-sized receptacle forthe molten metal.

The apparatus consists, essentially, of a tank of comparatively smalldimensions,having eX- tended downward from its bottom a tube ofsuflicient length to receive the articles to be coated when plunged downthrough the molten metal in the said tank and into the said tube, and inpractice the tube is preferably filled with molten lead, while the maintank or vessel above is filled with moltenzinc, which, being of lessspecific gravity, floats upon the top of the lead. The tube extends up ashort distance above the bottom of the tank, which is also covered withlead for a small depth, and the'dross, being heavier than the zinc, willaccumulate around the top of the tube and rest on the lead near thebottom of the tank below the zinc. The tube is heated by a fire in afurnace at its lower end, having a flue which surrounds the tube, and isprovided with means for regulating the temperature, which is maintainedat the proper height for keeping the lead in a molten state, and anotherfurnace is provided for the tank containing the zinc, in which a hottertire is maintained, as is necessary on account of the higher temperaturerequired for the fusion of zinc. The articles to be galvanized are thusplunged wholly through the bath of zinc and into thelead, and then onbeing withdrawn pass through the zinc again, they being exposed to thezinc last. Molten zinc is found to have a very destructive effect uponthe iron tanks containing it, and in order to obviate the necessity offrequent renewals of the tank the latter is, in accordance with thepresent invention, provided with an internal jacket or wall extendingnearly to the bottom of the tank, and the space between the saidinternal wall or jacket and the side wall of the tank is filled withlead,so thattheinner surface of the tank is acted upon only by the lead,which has but little, if any, destructive ei'fect on the iron. WV henthe jacket is eaten away or destroyed by the zinc,it is a comparativelyeasy matter to renew it.

The drawing shows in vertical section an apparatus for coating metalsembodying this invention.

The receptacle for containing the bath of molten metal in which thearticles to be coated are dipped consists of amain tank or reser- Voir,a, preferably of wrought-iron, supported in the upper portion of themasonry b of the furnace, and having a long extension or auxiliaryreservoir, 0, shown in this instance as a tube extending verticallydownward from around the tube 0, as indicated by the arrows,

thus maintaining the said tube at the proper temperature to fuse thematerial in it, the said material being preferably lead,which fuses atlower temperature than zinc,which is to form the main coating of thearticles. Suitable .doors or dampers, f, are provided for the admissionof cold air into the flue e, to regulate the temperature of the tube 0,the fire in the furnace d being kept quite low, or at about a red heat.The masonry b,near its upper end, is provided with another furnace, g,the fire in which acts upon the main tank a, and is kept at a high heat,as is required for melting the material in the said tank, which is inthis instance zinc. The upper end of the tube 0 extends above the bottomof the tank a, .as shown at 0, so that the dross or impurities from themetal that are heavier than zinc will accumulate around the sides of thesaid tube near the bottom of the tank a, as shown at h, thus leaving acolumn of clear liquid metal in the line of the tube through which thearticles being dipped pass.

In order to prevent the rapid destruction of the tank a by theamalgamating action of melted zinc, it is provided with a bottomlessinternal jacket or wall, 2', and the space between the said jacket andthe side wall of the tank is filled with lead, which also covers thebottom of the tank for a slight depth, as shown at k, floating the drossh, so that the entireinner surface of the tank a is exposed only to theaction of melted lead,which does not affect it. When the jacket iswholly eaten away by the action of the zinc,itmay be easily removed andanother one substituted at far less expense than would be required forproviding a new tank a, and it will be seen that the jacket t merely hasto separate the two liquid metals, the pressures of which about balanceone another, so that the jacket may be used when it would be much toothin to safely contain the entire mass of molten metal.

In operation the articles to be coated, having been previously treatedby acids or otherwise to prepare their surfaces to receive the coating,are thrust down through the melted zinc in the tank a into melted leadin the pipe 0, and then, upon being withdrawn, again pass through thezinc, so that the coating on the surface is mainly zinc, although theslight amount of lead that is alloyed with it is rather beneficial thanotherwise.

It will be seen that by an apparatus of this kind a comparatively smallbody of zinc in the tank a may be caused to act upon the entire surfaceof an article having one of its dimensions much greater than anydimension of the said tank, and that consequently articles may beproperly coated which by the usual method require a very large tank, andconsequently a very large body of melted zinc, which would require alarge expenditure of fuel to maintain it at the proper temperature.Thelong articles entering the melted zinc endwise disturb but a smallportion of its surface, and it is comparatively easy, when withdrawingthe said articles, to keep the said small portion of the surface of thebath clean and free from dross, so that a smooth and perfect coating isdeposited on the surface of the articlevbeing coated. The main functionof the tube 0 is to form a receptacle to receive the articles, so as toenable them to be drawn through the bath of molten metal above thesaidtube, and the lead in the tube forms a support for the metal in thetank, it requiring less fuel to keep the lead in a molten state than ifthe zinc filled the entire receptacle,

composed of a tank and tube; and, furthermore, as before stated, thepresence of the lead in the coating of the articles is rather beneticialthan otherwise. The part of the tube 0 passing through the furnace 9 maybe protected by masonry or fire-brick, and the said tube, being exposedto a comparatively low heat at its outer side and to the action ofmelted lead on its inner surface, will last a very long time.

While an apparatus of this kind is especially adapted for the treatmentof articles having one large dimension, it is also advantageous even forsmall articles-such as bolts, nuts, &c.-that can be wholly contained inthe main tank, as the presence of the vertical body of metal in the tubeis found to have a tendency to equalize the temperature of that in thetank, preventing it from too great cooling when a considerable mass ofcold metal is immersed in it.

It is obvious that the extension 0, herein shown as a tube, may be ofany desired shape in crossesection, and also that it may in some casesbe desirable to have two or more such extensions from different parts ofthe bottom of the main tank.

We claim- 1. The main tank or reservoir, combined with the auxiliaryreservoir extending downward from the bottom thereof, and having itsupper end projectingabove the bottom of the main tank, substantially asand for the pur pose described.

2. The main tank or reservoir, combined with a bottomless internaljacket adjacent to the side walls of the said reservoir, the spacebetween the said tank and jacket containing one molten metal, which alsocovers the bottom of the main tank, and the tank within ,the said jacketcontaining a different molten metal of less specific gravity,substantially as names to this specification in the presence ofdescribed. two subscribing Witnesses.

3. The main tank and auxiliary reservoir extending downward from thebottom thereof, 5 combined with independent furnaces for heating thesaid tank and auxiliary reservoir sub- Witnesses:

G. WV. GREGORY, \V. H. SIGsTON.

stantialiy as described.

In testimony whereof We have signed our

